The rapid development of terrestrial network technologies and the increasing complexity of space missions have generated a strong demand to extend the internet to space and to establish an integrated space-ground network system, and technologies today have already provided feasibility for doing so. The current situation in China is that space-ground protocols are not unified for different spacecraft in spaceflight missions. Space mission data can not be shared and the integrated data utilization ratio is still low. This paper analyzes the demand of future space missions and demonstrates the significance for China to develop its integrated space-ground network system. Status quo of space-based network system abroad is introduced. A concept on the overall objective, composition, network system architecture, and network protocols is proposed. Some key technologies are analyzed. Finally, suggestions are given regarding the steps of development.